pb

I am sure many of you had read my other thread, "Camshaft and Reversion". The general concensus from the board and others I have talked to in the industry is that the cam will not cause reversion.

If this is true then why would the intake valves and seats be extremely pitted. The exhaust valves and seats are fine.

Opinions please. This one is stumping me as well.

Thanks
Paul

robyw1

That stumps me too. Any chance you can send me a picture? And is this on all of your intake valves? any corosion on the valves? I have not read your other thread but I will go to it.

Roby

SSComp

Burning and pitting are generally caused by the valve failing to seat tightly, permitting exhaust blow-by. This condition is often caused by hard carbon particles on the valve seat. It may also be due to weak valve springs, insufficient tappet clearance, warpage and misalignment. Warpage occurs chiefly in the upper valve stem due to its exposure to intense heat. Out-of-round wear follows when the seat is pounded by a valve whose head is not in line with the stem and guide. Oil and air are sucked past worn intake valve stems and guides into the combustion chamber, causing excessive oil consumption, forming carbon and diluting carburized fuel.


Do you know what valves are in it? Unless they're very high quality they won't last long.

cuda

I think it's from bringing in the moist air. On salt water engines, you can tell even more. I don't want to talk about pitted valves right now. I pulled the valves out of a SBC I building yesterday, and the valve stems are pitted from just sitting too long.

Cord

iTrader: (2)

Which valves are pitted? Certain cylinders or all of them? Were the plugs washed clean? What was the condition of your intake gasket?

SSComp

Lets take a few steps back. What kind of engine is it and what changes have been made. I sure sounds like you've got a tired engine that needs a top overhaul at the very least.

I PM you my number feel free to call (no I'm not a mechanic nor do I want to sell you anything)

pb

ALL intake valves and seats are pitted. As far as I know, the valves are stock. The motor is a 1997 454 Mag that was massaged in 2000 with the cam in question from my other thread. Engine hours were 198 when test driven. Intake gasket was intact when intake was removed, however the intake manifold bolts in my opinion were not torqued properly. I broke them loose with a standard allen wrench.

Paul

Dennis Moore

The exhaust valves are stainless steel and the intake valves are not. The stainless steel exhaust valves won't rust or pit as quickly as the standard steel intake.
The exhaust seats are induction hardened by the factory for unleaded gasoline. The intake seats are usually not because they run much cooler. Have the exhaust seats been replaced with hardened inserts?

Your problem is not uncommon on a marine engine especially if the last guy that ground the valves did a sloppy job.

Dennis Moore

pb

Dennis,
The heads were reworked back in 2000. To what extent I am not sure. Still trying to obtain that info.

The heads were then pulled again approx. 1 yr ago due to a valve seat problem.

Excuse my ignorance, but how does sloppy valve grinding cause valve and seat pitting?

Would hardened seats not pit? Should the intake seats be replaced with hardened seats.

Since it is all apart, I want to cover all the bases so it is done correctly as to not have to go through it again in the near future.

Paul

Dennis Moore

One really bizarre thing that happened to me (after I had the valves ground on an engine) was that it was getting water into the cylinders. I couldn't figure out were it was coming from. I pulled the exhaust manifolds to inspect the exhaust ports and found nothing. I pumped up the cooling system with air pressure and just happened to look inside the exhaust ports. Water was weeping out from between the valve guide/valve stem area and running into the cylinder when the valve was open. I removed the heads and the valves. With a flashlight I could see slight cracks in the valve guides. I had my machinest push out the valve guides (they are replaceable and pressed into a BB Chevy head). They were rusted through! The valve guides on a big block sit inside the water cooling passage of the head. I felt the heads must be rusted in other places as well and we replaced them.

If the valve guides were replaced incorrectly and/or are leaking on your engine, a little water could be seeping through and rusting and pitting your valves and seats. A long shot, but something that happened to me.

Dennis Moore